<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <!-- 外联样式 -->
    <link rel="stylesheet" href="theme.css">
    <!-- 内嵌样式 -->
    <style>
        .text p {
            color: red;
        }
        div p {
            color: blue;
        }
        #main p {
            color: green;
        }
        .container #main p {
            color: orange;
        }
        .btn {
            background: black;
        }
    </style>
</head>
<body>
    <div class="text">
    <p>Hello</p>
    </div>

    <div class="container">
        <div id="main">
        <p>Hello</p>
        </div>
    </div>
    <!-- 行内样式 少用 -->
    <button class="btn" style="background: pink;">Click</button>
</body>
</html>